document how to map a service back to an underlying host

Let's say check.tpo goes down, and is unpingable. That means something has probably gone wrong with the underlying host. How do I learn what underlying server is serving check.tpo?

It would be great to have that process, of mapping a service back to which host it's on, written down, either on https://help.torproject.org/tsa/ or pointed to from there.

Thanks!